Field of the Invention
The invention is directed to the field of electro-optic devices and components and, more particularly, to a transceiver module including an optical transmitter and an optical receiver in a single housing minimizing electromagnetic radiation emerging from the enclosures leading to electromagnetic interference (EMI).
In communication applications like Local Area Networks (LAN), Metropolian Area Networks (MAN) and Wide Area Networks (WAN) optical transmitters and receivers are widely used for two way communications. Therefore an optical transmitter and receiver are often combined within one housing defining a so-called optical transceiver module.
Optical LANs shall provide a large number of two-way links to the customer. This is why optical transceiver modules shall desireably be relatively small because a high port density can be achieved in an apparatus employing a large number of transceiver modules. Thus one first desired goal is the miniaturization of optical transceiver modules.
Due to the increasing demand for transmission bandwidth operating Bit-rates for optical networks are increasing steadily. Therefore the electronic circuits of both the optical transmitter and receiver are emitting electromagnetic radiation of higher frequencies as well. Due to the desired miniaturization and to the increasing operating frequencies in the range of several hundred MHz and more, portions of the housing may act like antennas provided the length of the portions matches to the wavelength of the emitted electromagnetic radiation. These antenna-portions of the housing will then re-radiate the electromagnetic waves amplifying the amount of electromagnetic radiation emerging from a transceiver module.
This leads to the problem of electromagnetic interference (EMI) both between the electronic circuits inside the housing of the transceiver module and between the electronic circuits inside the housing and further electronic circuits and devices outside the housing.
Due to existing agency standards regulating the amount of EMI for electronic equipment much attention has to be paid to EMI shielding of such transceivers.
In the art several approaches to solve this problem are proposed. In U.S. Pat. No. 5,047,835 Chang discloses an optical transceiver comprising an EMI shield covering both the electrical circuit of the transmitter and the receiver.
U.S. Pat. No. 5,117,476 to Yingst et al. discloses an optical transceiver including a common horizontally extending circuit board with individual EMI shields over the transmitter and receiver circuit portions.
Taniguchi discloses in U.S. Pat. No. 5,535,034 an optical transceiver capable of preventing any crosstalk from an optical transmitter to an optical receiver comprising a multilayer printed circuit board and two regions that are completely isolated electromagnetically from each other for the transmitter and the receiver respectively.
In the prior art operating optical frequencies are limited in the region of several hundred MHz because after transducing optical signals of higher frequencies in the range of several GHz and more to electrical signals, it becomes technically difficult to avoid large scale electromagnetic interference effects on printed circuit boards.